JPS6345500B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention detects the air-fuel ratio based on the exhaust components of an engine such as an automobile, and uses this detection signal to feedback control the air-fuel ratio of the air-fuel mixture supplied to the engine to a predetermined air-fuel ratio. This invention relates to a fuel ratio control method.

A conventional air-fuel ratio control method involves integrating the output of an air-fuel ratio sensor and performing simple integral control using this integrated signal. Therefore, during transient engine operation, if the basic air-fuel ratio changes faster than the correction speed of the integral control, the correction cannot catch up. Further, when the air-fuel ratio sensor is inactive, feedback control of the air-fuel ratio cannot be performed, and sufficient air-fuel ratio control cannot be performed, resulting in deterioration of exhaust gas. In other words, such a control method is good when the engine is operating in a relatively stable operating state, but it is difficult to learn in other acceleration ranges where a large amount of harmful exhaust gas components are emitted, so the correction speed of integral control is It cannot keep up with fluctuations in the basic air-fuel ratio, resulting in deterioration of exhaust gas. This problem is particularly noticeable in a fuel injection device in which the amount of fuel supplied is programmed based on intake pipe pressure and rotational speed, or in a fuel injection device in which the amount of fuel supplied is programmed based on throttle valve opening and rotational speed.

Also, to elaborate more on the fuel injector when programmed with intake pipe pressure and rotational speed:
The main factors that cause an error between the basic air-fuel ratio and the target air-fuel ratio are (1) changes over time or production variations in the tappet clearance of the engine's intake and exhaust valves, (2) production variations and changes over time in the injector, (3) ) Changes in atmospheric pressure (for example, when driving at high altitudes).

Through investigation, the inventors have found that the errors caused by these three factors vary depending on the operating conditions.

The error due to factor (1) is largest at idle;
The larger the intake pipe pressure is in terms of absolute value, and the higher the rotation, the smaller it is.

The error due to factor (2) becomes larger as the load becomes smaller (lower intake pipe pressure), and becomes smaller as the load becomes larger.

The error due to factor (3) remains the same regardless of the operating conditions.

Therefore, when errors due to three factors occur simultaneously, the error due to factor (1) is dominant in the idle state, and the error due to factor (2) is dominant in the light load operating state. It was also found that the error due to factor (3) becomes dominant under high-load operating conditions.

An object of the present invention is to improve the conventional integral control method of the air-fuel ratio using the output signal of an air-fuel ratio sensor, and to quickly and without delay in response even during engine transients.
The air-fuel ratio can be controlled to a predetermined air-fuel ratio, and even when the air-fuel ratio sensor is inactive when the engine is at low temperature and feedback control cannot be performed, the air-fuel ratio can be accurately controlled based on the engine condition correction amount stored in the storage device. An object of the present invention is to provide a fuel ratio control method.

In the present invention, the predetermined basic fuel injection amount is directly determined by the integral correction value that is obtained by integrating the output signal of the air-fuel sensor and that varies upward and downward around a predetermined value that represents a state that does not require air-fuel ratio correction. Without correction, the integral correction value is first decreased or increased for a predetermined operating state in the engine operating range, that is, the idle state, depending on whether the integral correction value is larger or smaller than the above-mentioned predetermined value. The engine condition correction amount is calculated, and the fuel green amount is corrected using this engine condition correction amount to control the injection valve. In this case, the engine condition correction amount is calculated by multiplying the basic fuel injection amount by a coefficient _k2 that decreases or increases around a predetermined reference value depending on whether the integral correction value is larger or smaller than a predetermined value. Furthermore, it is determined by multiplying the intake pipe negative pressure, which indicates the load, by a coefficient C, which is inversely proportional to the engine speed.

In addition, among the engine condition correction amounts, the idle state correction amount uses a coefficient C which is inversely proportional to the intake pipe pressure and rotational speed at the same time as the coefficient _k2 , so the correction amount becomes small in areas of high rotation and load, so the tappet clearance can be reduced. Appropriate corrections can be made in response to changes.

The present invention will be explained below with reference to the drawings.

In FIG. 1, an engine 1 is a known four-stroke spark ignition engine mounted on an automobile, and intakes combustion air through an air cleaner 2, an intake pipe 3, and a throttle valve 4.

Further, fuel is supplied from a fuel system (not shown) through electromagnetic fuel injection valves 5 provided corresponding to each cylinder. The exhaust gas after combustion is discharged into the atmosphere through an exhaust manifold 6, an exhaust pipe 7, and a three-way catalytic converter 8. The pressure downstream of the throttle valve in the intake pipe 3 is measured by a known semiconductor pressure sensor 11 (intake pipe pressure sensor).
Detected by The pressure sensor outputs an analog voltage signal. Furthermore, the intake pipe 3 has an intake air temperature sensor 1 that detects the temperature of the air taken into the engine.
2. A water temperature sensor 13 is installed in the engine 1 to detect the cooling water temperature. Furthermore, the exhaust manifold 6 detects the air-fuel ratio from the oxygen concentration in the exhaust gas, and when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich), it is about 1 volt (high level), and when it is larger than the stoichiometric air-fuel ratio (lean), it is about 0.1 volt. An air-fuel ratio sensor 14 that outputs a low level voltage is installed. The rotational speed sensor 15 detects the rotational speed of the crankshaft of the engine 1 and outputs a pulse signal with a frequency corresponding to the rotational speed. The control unit 20 is a circuit that calculates the fuel injection amount based on the detection signals of the sensors 11 to 15, and controls the opening time of the electromagnetic fuel injection valve 5, thereby adjusting the agricultural injection amount.

The control unit 20 will be explained with reference to FIG.

100 is a microprocessor (CPU) that calculates the fuel injection amount. A rotation speed counter 101 counts the engine rotation speed based on a signal from the rotation speed sensor 15. Further, this rotation number counter 101 is synchronized with the engine rotation, and the interrupt control unit 1
Send an interrupt command signal to 02. Interrupt control unit 102
When receiving this signal, it outputs an interrupt signal to the microprocessor 100 via the common bus 150. Reference numeral 103 is a digital input port that inputs digital signals to the microprocessor 100, such as an output signal from a comparator that compares the output of the air-fuel ratio sensor 14 with a predetermined comparison level, and a starter signal from a starter switch 16 that turns on and off the operation of a starter (not shown). introduce.

104 is an analog input port consisting of an analog multiplexer and an A-D converter; an intake pipe pressure sensor 11, an intake air temperature sensor 12, and a cooling water temperature sensor 1.
The microprocessor 100 has a function of converting each signal from the microprocessor 100 into digital data and sequentially reading the signals into the microprocessor 100. Output information from each of these units 101, 102, 103, and 104 is transmitted to the microprocessor 100 through a common bus 150. A power supply circuit 105 supplies power to a RAM 107, which will be described later. 17
18 is a battery, and 18 is a key switch, but the power supply circuit 105 is directly connected to the battery 17 without passing through the key switch 18. I will explain later
Power is always applied to the RAM 107 regardless of the key switch 18.

106 is also a power supply circuit, which is connected to the battery 17 through the key switch 18. The power supply circuit 106 supplies power to parts other than the RAM 107, which will be described later. 107 is a temporary storage unit (RAM) that is used temporarily during program operation.
As mentioned above, power is always applied regardless of the key switch 18, and the memory contents are not lost even if the key switch 18 is turned off and the engine operation is stopped, thus forming a non-volatile memory. The engine condition correction coefficients k ₁ , k ₂ , k ₃ described later are also stored in this RAM 10.
7 is memorized.

A read-only memory (ROM) 108 stores programs, various constants, and the like. 10
Reference numeral 9 is a fuel injection time control counter including a register, which is configured to count down, and is operated by a microprocessor (CPU) 100.
A digital signal representing the opening time of the electromagnetic fuel injection valve 5, that is, the amount of fuel to be injected, is converted into a pulse signal having a pulse duration giving the actual opening time of the electromagnetic fuel injection valve 5.

Reference numeral 110 denotes a power amplification unit that drives the electromagnetic fuel injection valve 5. 111 measures the elapsed time with a timer.
The information is transmitted to the CPU 100. Rotation number counter 101
measures the engine rotation speed once per engine rotation based on the output of the rotation speed sensor 15, and supplies an interrupt command signal to the interrupt control section 102 at the end of the measurement. The interrupt control section 102 generates an interrupt signal from the signal, and causes the microprocessor 100 to execute an interrupt processing routine for calculating the fuel injection amount.

FIG. 3 shows a schematic flowchart of the microcomputer 100, and the functions of the microcomputer 100 will be explained based on this flowchart. When the key switch 18 and starter switch 16 are turned on to start the engine, the main routine arithmetic processing starts at the start of the first step 1000, initialization processing is executed at step 1001, and analog input port is opened at step 1002. Digital values corresponding to the cooling water temperature and intake air temperature are read from 104. In step 1003, a correction value _kl is calculated using a known formula based on the result, and the result is
Store in RAM107. In step 1004, the signal of the air-fuel ratio sensor 14 is inputted from the digital input port, and the integral correction value _K2 , which will be described later, is increased or decreased as a function of the elapsed time by the timer 111 _.
is stored in the RAM 107. Figure 4 shows the processing steps for increasing/decreasing this integral correction value _K2 , that is, integrating it.
1004 detailed flowchart. First, in step 400, it is determined whether the air-fuel ratio detector is activated or whether feedback control of the air-fuel ratio is possible based on the cooling water temperature, etc. If feedback control is not possible, that is, in the case of an open loop, the process proceeds to step 406. The correction value K ₂ is set to K ₂ =1, and the process proceeds to step 405. If feedback control is possible, proceed to step 401. step
401 measures whether the elapsed time has passed unit time △t ₁ ,
If it has not passed, this processing step 1004 is terminated without performing the integral processing of _K2 . If the time Δt ₁ has elapsed, the process proceeds to step 402, and if the air-fuel ratio is rich and the output of the air-fuel ratio sensor 14 is a rich high level signal, the process proceeds to step 403, where the results obtained in the previous cycle are performed. Decrease solid K ₂ by △K ₂ ,
Proceed to step 405 and save the new correction value _K2 to RAM1.
Store in 07. In step 402, if the air-fuel ratio is lean and the output of the air-fuel ratio sensor 14 is a low level signal indicating lean, the process proceeds to step 404, where _K2 is increased by _ΔK2 , and the process proceeds to step 405. In this way, the correction value _K2 is increased or decreased. In this way, the integral correction value _K2 changes above and below a predetermined value representing a state in which air-fuel ratio correction is not required.

In step 1005 of FIG. 3, the coefficients k ₁ , k ₂ , and k ₃ for calculating the engine condition correction amount are increased or decreased.
The result is stored in RAM 107.

In FIG. 5, coefficients k ₁ , k ₂ and k ₃ are processed and stored. That is, this is a detailed flowchart of step 1005 for memory processing.

In step 501, it is determined whether the elapsed time has passed the unit time _Δt2 , and if the unit time _Δt2 has not passed, the memory processing step 1005 is ended. If the engine speed has elapsed, the process advances to step 502, where the rotational speed N and intake pipe pressure P stored in the RAM 107 are set to the operating conditions (600<N<900rpm, 200<P<400mm) representing the idle state.
Hg). When the described operating conditions are met, the process proceeds to step 503, where the value of the integral correction value _K2 is determined. If K ₂ =1, nothing is done and this process step 1005 ends. If K ₂ >1 in step 503, the process proceeds to step 504, and if K ₂ <1, the process proceeds to step 505. In steps 504 and 505, △k ₂ is added or subtracted from the coefficient k ₂ , and in step 506, the newly obtained k ₂ is stored in the RAM 107, and the step
End 1005.

If the stated conditions are not met in step 502, the process proceeds to step 507, where it is determined whether the rotational speed N is within the range of 1400 to 3000 rpm, which represents a steady running condition.If it is not within this range, no processing is performed at step 1005, and the process ends. do. When it is within the range of 1400 to 3000 rpm, the process proceeds to step 508, where it is determined whether the intake pipe pressure P is within the range of 250 to 400 mmHg, which represents the normal load, and when it is within the above range, the process proceeds to step 509. Intake pipe pressure P
is not in the range of 250 to 400 mmHg, the process proceeds to step 513, and the intake pipe pressure P is set to 400, which indicates a high load.
Determine if it is within the range of ~650mmHg. If it is not in the above area, no processing is performed and this step 1005 is ended.

In step 509, the value of the integral correction value _K2 is determined. If K ₂ = 1, do nothing and skip this processing step.
End 1005.

If K ₂ >1, proceed to step 510; if K ₂ >1, proceed to step 511. In steps 510 and 511, Δk ₃ is added to or subtracted from the coefficient k _3. In step 512, the newly obtained coefficient k ₃ is stored in the RAM 107, and step 1005 is ended.

When the intake pipe pressure P is between 400 and 650 mmHg, the process proceeds to step 514, where the value of the integral correction value _K2 is determined.

If K ₂ = 1, do nothing and skip this processing step.
End 1005.

If K ₂ >1, proceed to step 515; if K ₂ <1, proceed to step 516. In steps 515 and 516, Δk ₁ is added to or subtracted from the coefficient k ₁ , and in step 517, the newly obtained coefficient k ₁ is stored in the RAM 107, and step 1005 is ended.

Normally, the main routine processes 1002 to 1005 are repeatedly executed according to the control program. When an interrupt signal for fuel injection amount calculation is input from the interrupt control unit 102, the microcomputer 1
00 immediately interrupts the main routine processing even if it is in progress and moves to the interrupt processing routine at step 1010. In step 1011, revolution counter 1
In step 1012, a signal representing the intake pipe pressure P is taken in from the analog input port 104, and in step 1013, the engine speed N and intake pipe pressure P are input as main signals. For use in routine calculations
Store in RAM107. Next, in step 1014, the basic fuel injection amount Tp (that is, the injection time width of the electromagnetic fuel injection valve 5), which is preprogrammed in the ROM 108 as a two-dimensional map of the engine speed N and the intake pipe pressure P, is calculated by interpolation. and ask. Next, in step 1015, various correction values and correction coefficients for fuel injection obtained in the main routine are
It reads out from the RAM 107 and performs correction calculation of the injection amount (injection time width) that determines the air-fuel ratio. The calculation formula for the injection time width T is T={(1+k ₁ +k ₂ *C)*Tp+k ₃ }*K ₁ *K ₂ .

As can be seen from this formula, (1 + k ₁ + k ₂ * C) * Tp + k ₃ is an engine state correction that adds the engine state correction amount calculated based on the three correction coefficients k ₁ , k ₂ , and k ₃ to the basic injection amount. It represents the injection amount, of which k ₁ *Tp is the steady running high load state correction amount, k ₂ *C*Tp is the idling state correction amount, and k ₃ is the steady running normal load correct amount. Further, C is given as a function of intake pipe pressure P and rotational speed N by the following calculation formula: C=C ₀ /P*N (C ₀ is a constant).

Next, in step 1016, data on the corrected fuel injection amount T is set in the counter 109. Next, the process advances to step 1017 to return to the main routine. When returning to the main routine, the process returns to the processing step at which it was interrupted due to interrupt processing. The general functions of the microprocessor 100 are as described above.

As described above, since the fuel amount is corrected using the engine state correction amount _k2 updated when the engine is idling, it is possible to finely correct deviations in the basic air-fuel ratio. For example, according to the inventor's research, the deviation in the basic air-fuel ratio due to changes in the tappet clearance of the intake and exhaust valves is largest at idle, and becomes smaller as the rotation or load becomes higher. k ₂ is for idle conditions (rotation 600~900rpm, intake pipe pressure 200~400mm)
hgabs), and when actually correcting it, k ₂ *
Since the correction is made with the correction amount C ₀ /P*N, the correction amount is small in areas of high rotation and high load, and it is possible to appropriately correct in response to changes in the tappet clearance.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram of an apparatus for explaining an embodiment of the present invention, FIG. 2 is a block diagram of the control circuit shown in FIG. 1, and FIG. 3 is a schematic diagram of the microprocessor shown in FIG. Flowchart: FIG. 4 shows a detailed flowchart of step 1004 shown in FIG. 3, and FIG. 5 shows a detailed flowchart of step 1005 shown in FIG. In the figure, 1...engine, 5...fuel injection valve, 11...intake pressure sensor, 14...air-fuel ratio sensor, 15...rotational speed sensor, 20...control unit.

Claims (1)

[Claims] 1. A method comprising an air-fuel ratio sensor that detects an air-fuel ratio based on engine exhaust gas components, and controlling the air-fuel ratio of a mixture supplied to the engine to a predetermined air-fuel ratio based on a signal from the air-fuel ratio sensor. A first correction value is obtained by integrating the signal from the air-fuel ratio sensor, and an engine condition correction value that is always stored in a storage device is applied to the first correction value when the engine is in an idle state. the updated and stored engine condition correction value is converted to a value that decreases as the engine load increases, and the basic fuel amount to the engine is corrected based on this conversion value and the first correction value. . An air-fuel ratio control method, characterized in that the corrected fuel amount is supplied to the engine. 2. The air-fuel ratio control method according to claim 1, wherein the basic fuel amount is corrected by multiplying the basic fuel amount by the converted value and the first correction value.